Re: [PATCH v2 2/2] iio: light: Add Capella CM3217 ambient light sensor driver

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 06 Nov 2026 21:56:30 +0100
Patrick Fischer via B4 Relay <devnull+admin.tsv-stahl-riesa.de@kernel.org> wrote:

> From: Patrick Fischer <admin@tsv-stahl-riesa.de>
> 
> The CM3217 has no registers and no ID. Writing a byte to address 0x10
> or 0x11 sets command byte 1 or 2, reading a byte from 0x10 or 0x11
> returns the high or low byte of the 16-bit light count.
> 
> Command byte 1 holds the shutdown bit and the IT_T field (1/2 T, 1 T,
> 2 T or 4 T), command byte 2 the FD_IT field (800 ms down to 66 ms). The
> count scales linearly with both. The driver exposes FD_IT as the
> integration time and IT_T through the scale, so the scale list offers
> four ranges for each integration time.
> 
> The datasheet is not public. The bit fields, the reserved bits that are
> written as 1 and the startup setting of 2 T and 100 ms come from NVIDIA's
> downstream drivers (drivers/staging/iio/light/cm3217.c in the 3.4 kernel
> rel-tegranote-r8 and the 3.10 kernel
> android-tegra-flounder-3.10-nougat-mr1.1). One value differs: the vendor
> header defines 4 T as 4 << 2, which is outside the two-bit field. On a
> Tegra Note 7 field value 3 gave four times the 1 T count, so the driver
> uses that. For the resolution, Capella
> gives a range of 0.01875 to 119156 lux. The driver takes 0.01875 lux
> per count at 4 T and 800 ms. This matches both the upper end (65535
> counts at 1/2 T and 66 ms) and the 0.3 lux per count that the NVIDIA
> 3.4 driver uses at 2 T and 100 ms.
> 
> The sensor has no data-ready flag, and a new setting only takes effect
> when the conversion in progress ends. A conversion takes IT_T times
> FD_IT, up to 3.2 s. Leaving shutdown starts a new one at once, so the
> driver passes through shutdown on every change and waits one conversion
> period plus a margin before it reads the count. The timing was measured
> on a Tegra Note 7.
> 
> Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # Tegratab P1988
> Signed-off-by: Patrick Fischer <admin@tsv-stahl-riesa.de>
Hi Patrick,

This looks good to me.

I won't pick it up just yet though as need to allow time for
dt-binding review and for anyone else who is interested to take
a look.

Thanks,

Jonathan